In situ hybridization with non-radioactive digoxigenin-11-UTP-labeled cRNA probes: Localization of developmentally regulated mouse tenascin mRNAs

An improved method for in situ hybridization was developed in order to identify the tissue-specific expression of messenger RNA (mRNA) for the novel extracellular matrix glycoprotein, tenascin, during mouse development. Non-radioactive RNA probes were generated by incorporating digoxigenin-11-UTP instead of conventional isotopic labels. Hybridization of anti-sense probes to complementary mRNAs was detected by a chromogenic staining reaction catalyzed by an anti-digoxigenin antibody-alkaline phosphatase conjugate. Markedly improved enhancement of staining was achieved by expanding the complexity of probes and strictly controlling the degree of proteolytic digestion of paraformaldehyde-fixed tissue sections. Six different complementary RNA (cRNA) probes representing most of the tenascin mRNA sequence were prepared. Very weak signals were obtained after single applications of each probe, but strong specific signals were present when all six probes were mixed together. In either case, no signal was found without prior proteolytic digestion of tissue sections with proteinase K. Treatment with increasing concentrations of proteinase K initially resulted in increased sensitivity of signal detection, but extensive digestion resulted in histological sections of poor quality for light microscopy. Optimal conditions varied according to the tissue type examined. In lung, in situ hybridization detected tenascin mRNA in the relatively large cells lining alveolar walls adjacent to type I pneumocytes. In cerebellum, glial cells of the Purkinje cell layer lining contained tenascin mRNA, but Purkinje cells did not. In both cases, hybridization signals were confined to the cytoplasm of cells, and no extracellular staining was observed. This method provides a promising new tool for analysis of spatio-temporal regulation of tenascin gene expression during embryogenesis and oncogenesis.